1. Field of the Invention
The invention relates to a fuel injection control device of an internal combustion engine. Particularly, this invention relates to a fuel injection control device of an internal combustion engine that is provided in an internal combustion engine that has a fuel injection devices that supply fuel by the injection to intake ports and the injection into cylinders.
2. Description of the Related Art
An internal combustion engine in the related art is equipped with in-cylinder fuel injection means for injecting fuel directly into cylinders of the internal combustion engine. During operation of the internal combustion engine, fuel is supplied by the in-cylinder fuel injection means. However, during operation of the internal combustion engine, the pressure in each cylinder continues fluctuating. Therefore, in the case where fuel is directly injected into the cylinders, a desired manner of injection of fuel may not be able to be achieved due to the effect of fluctuations in the in-cylinder pressure. For example, in the case where an internal combustion engine is provided with a fuel injection valve that injects fuel into a cylinder, as in-cylinder fuel injection means, the amount of fuel injected from the fuel injection valve into the cylinder may change due to the effect of fluctuations in the in-cylinder pressure.
Concretely, in an internal combustion engine as described above, in which fuel is injected during the intake stroke or the compression stroke, the in-cylinder pressure becomes low during the intake stroke, and becomes high during the compression stroke. Therefore, in the case where fuel is injected to a cylinder at a constant pressure, the amount of fuel injected tends to be larger if fuel is injected during the intake stroke than if fuel is injected during the compression stroke, and thus fuel may not be able to be injected in a desired amount. Hence, there is a possibility that it may become difficult to control the amount of fuel injection with good accuracy, and the fuel economy performance and the exhaust gas purification performance may reduce.
Therefore, in some internal combustion engines in the related art, the effect of fluctuations in the in-cylinder pressure on the amount of fuel injection is reduced. For example, in a fuel control device of an engine described in Japanese Patent Application Publication No. 2001-98973, when fuel is injected during the intake stroke, the duration of the fuel injection by the fuel injection valve is made relatively short during a period from the vicinity of a crank angle at which the descent speed of the piston reaches its maximum until a predetermined crank angle. This restrains excessive increase of the amount of fuel injection in the case where fuel is injected during the intake stroke, during which the in-cylinder pressure becomes low and therefore the amount of fuel injection is likely to become large. As a result, the amount of fuel injection can be controlled. Thus, the fuel economy performance and the exhaust gas purification performance are intended to be improved.
Furthermore, an internal combustion engine in the related art is equipped with in-intake passageway fuel injection means capable of injecting fuel into an intake passageway, and in-cylinder fuel injection means capable of injecting fuel into a cylinder, and thereby injects fuel into both the intake passageway and the cylinder, in order to improve the operation performance of the engine. In such an internal combustion engine, during an ordinary operation, the operation performance is intended to be improved by injecting appropriate amounts of fuel into the intake passageway and the cylinder in accordance with the state of operation. Besides, at the time of the cold start of this internal combustion engine, fuel is injected into the cylinder during the compression stroke so as to achieve an improvement in the startability and a decline in the emissions. That is, at the time of the cold start of the internal combustion engine, a mixture gas of fuel and air is stratified in the cylinder by injecting fuel into the cylinder during the compression stroke, so that the fuel in the mixture gas easily burns, and the startability of the internal combustion engine improves. Besides, since the startability of the internal combustion engine improves, the amount of fuel injection can be considerably reduced, and therefore the amount of HC (hydrocarbon) and CO (carbon monoxide) in exhaust gas can be reduced and the fuel economy can be improved.
However, the amount of fuel injection needed at the time of the cold start tends to be larger the lower the temperature. Therefore, at the time of the cold start, there is a tendency that the lower the temperature of the internal combustion engine or the external air, the larger the amount of fuel injected into the cylinder becomes, and the longer the injection duration becomes. As a result, the duration of the injection of fuel into the cylinder sometimes becomes longer than the time interval from the start timing of the injection of fuel into the cylinder during the compression stroke to the ignition timing. The fuel injection valves that inject fuel into cylinders, that is, injectors that inject fuel, and the like sometimes have variation in the injection characteristic. Furthermore, the fuel pressure that is the pressure of the fuel injected by the injectors also sometimes has some variation. Therefore, in the related-art internal combustion engines, there is a tendency of such variation being taken into account for the injection of fuel. Therefore, the duration of the fuel injection into the cylinder tends to become long due to the variation. This also sometimes results in the duration of the injection of fuel into the cylinder being longer than the time interval from the start timing of the fuel injection into the cylinder during the compression stroke to the ignition timing.
If the duration of the injection of fuel into the cylinder becomes longer than the time interval from the start timing of the fuel injection into the cylinder during the compression stroke to the ignition timing, fuel continues to be injected even after the ignition plug provided for the cylinder ignites. Therefore, there is a possibility of occurrence of irregular combustion or misfire due to a fuel-wet ignition plug. In that case, therefore, a related-art internal combustion engine switches the fuel injection manner from the fuel injection into the cylinder to the fuel injection into the intake passageway, and then injects fuel into the intake passageway during the intake stroke. However, in the case where fuel is injected into the intake passageway at the time of the cold start, the combustion of the fuel in the mixture gas around the ignition plug becomes more difficult than in the case where fuel is injected into the cylinder, and therefore, there is a possibility of decline in the startability. Therefore, there is a need to inject much fuel at the time of starting the engine, which leads to a possibility of deterioration of the emissions.